Method of deodorizing and sterilizing air in enclosed spaces



States 1 METHOD OF DEODORIZING AND STERILIZING AIR IN ENCLOSED SPACESRichard L. Kuehner and Neil E. Hopkins, York, Pa., assignors toBorg-Warner Corporation, Chicago, 111., a corporation of IllinoisApplication January 18, 1957, Serial No. 635,040

1 Claim. (CI. 21-53) and sterilization of the air circulated in airconditioning systems in accordance with the method described in theKuehner Patent No. 2,683,074, issued July 6, 1954, to one of the presentapplicants. As disclosed in said patent, an effective method ofproducing such a sterilization and deodorization consists in sprayingthe circulated air with a circulating aqueous alkaline solution ofpotassium permanganate. Such a solution has been found to be highlyeffective in removing odors, molds, and bacteria from the circulatingair. It is the object of this invention to improve the operation of thismethod so as to overcome certain drawbacks which have manifestedthemselves in the practical operation of the system. More particularly,it is the object of this invention (a) To eliminate the evaporation ofthe water component of the spray, and

(b) T o eliminate the necessity for a chemical charging device,sometimes referred to as a dispenser.

With regard to the first of the above objects, it will be recognizedthat, as in the case of a plain aqueous spray, the air passing through atreating unit in which it is sprayed with an aqueous solution ofpotassium permanganate is brought nearly to the saturation point; hence,in the absence of refrigeration or heating means in the unit, the airwould issue from the unit in a state close to saturation at the air wetbulb temperature. That is, the relative humidity in the room isincreased beyond the comfort zone. Obviously, this imposes severelimitations in the use of the treating unit. More particularly, itlimits the percentage of room air which can be circulated through thetreating unit in contrast to the total air going to the air conditioner,and even with this limitation, there is bound to be some rise inrelative humidity. Another drawback resulting from the evaporation liesin the necessity of providing a water make-up line to supply theequivalent of the water evaporated, and drain lines to guard againstaccidental overflow. Obviously, this limits the mobility of the unit andincreases appreciably the installation costs.

Regarding the second object of the invention referred to above, it willbe appreciated that, since the deodorant and disinfectant effect of thepermanganate treating solution is dependent upon a chemical reactionbetween the smoke, etc. in the air and the dissolved chemicals in thesolution, the chemicals are gradually consumed and, hence, must bereplaced. Moreover, in actual practice, it is found desirable tomaintain the concentration of the solution at a strength less thansaturation in order to obviate any tendency of the chemicals tocrystallize on the equipment and form deposits leading to the corrosionof the metallic surfaces, stopping of flow lines, etc;

Accordingly, in order to maintain the concentration of the treatingsolution at an optimum predetermined value less than saturation, it wasnecessary heretofore to pro:

atent 0 ice vide a suitable dispenser for automatically feeding at aretarded rate the chemicals into the treating solution, as the chemicalsdissolved therein became consumed by the treatment.

Applicants have discovered a practical and effective means forovercoming all of the drawbacks enumerated above, namely, undesired risein the humidity, necessity for a water-make-up line, and necessity for adispenser.

The nature and advantages of the present invention will be betterunderstood by reference to the accompanying drawings, in which Fig. 1 isa diagrammatic view of a typical washer adapted for carrying outapplicants invention;

Fig. 2 is a chart illustrative of the vapor pressure conditionsobtaining with the use of the present invention.

Referring to Fig. 1: The unit has the usual spray devices 10 forspraying the aqueous treating solution.

1 These are interposed in the path of the air stream which enters thecompartment 11 at one end 12 and leaves at the other end 13. Thesolution circulating means is indicated at 14, the solution accumulatingin the bottom of the compartment to the level indicated at 15.

In initially preparing the treating solution, the chemicals may be addedto the treating water in the compartment, or the water may bepreliminarily prepared by adding the chemicals thereto and introducingthe same to the circulating system. The chemicals may be intro duced tothe treating water individually or as mixtures in the form of drypowders, concentrated aqueous solutions or as pills or tablets,whichever is considered most convenient.

The numeral 16 indicates a suitable receptacle or retaining basket forreplenishing the chemicals in the solution, as they are consumed in thecourse of the operation of the unit, in order to maintain the desiredconcentration thereof. This receptacle can consist of a perforatedbasket containing a supply of chemicals submerged in the treatingsolution so that the latter has access to the chemicals. As will beexplained below, it is a feature of the present invention that therewill take place but a limited solution of the chemicals in the treatingsolution.

In accordance with the present invention, applicant add a controlledproportion of another salt, specifically lithium chloride, to theaqueous'solution of potassium permanganate. Applicants have establishedthat when this salt is present in the permanganate solution, it ispossible to operate at room temperature without humidifying the air inthe room. By reason of the presence of lithium chloride in controlledamounts, the vapor pres. sure of the aqueous spray solution becomes suchthat,

under all ordinary temperature and humidity conditions, water will notevaporate from the solution beyond a certain point and there will be nonecessity for a water make-up line.

As an aid in understanding the operation of an air treating system usingapplicants invention, reference is had to Fig. 2 which represents alithium chloride vapor pressure chart, reproduced from Chemical andMetallurgical Engineering 47 (5), page 303, May 1940. The' severalcurves in this chart show the relationship between dry bulb temperatureand the vapor pressure of lithium chloride solutions of variousconcentrations.

As is readily apparent from the chart, the vapor pressure of an aqueoussolution containing lithium chlo ride is less than the vapor pressure ofpure water at the same temperature (0% LiCl curve). The lithium chloridedepresses the vapor pressure to a degree dependent upon the percentageof this salt in the water solution. As

an example, let us assume that the air deodorizing system is to beoperated under conditions of dry bulb an,

he late and 0%. re atiye Intens ty oi the rose! air en ring the treatingunit. from available psychromet- J'ic data set out on the chart ofFigure 2, it is found that-the correspondingpartial pressnre of this airis 13 .1 m m y By e e enc t t ha Fi ure it will also be seen that the 80dry bulb temperature line (on the abscissa) intersects the 13.1 mm.mercury vapor pressure line (on the ordinate) at a point which lies on alithium chloride line corresponding to a solution concentration of 29%lithium chloride by weight. Hence, if 29% of lithium chloride be addedto the treating solution, then, the system would stabilize at this,condition and, thereafter, water vapor; would neither be evaporated fromthe solution nor condensed from the air stream.

Of course, changing conditions whether of temperature or humidity, orboth, of the air entering the unit would bring about a new equilibriumcondition with the lithium chloride water spray to balance out at a newconcentra-, tion in the spray solution. For example, let us assume thatthe air supplied to the unit changes from 80 dry bulb, 50% relativehumidity,-i. e. the conditions of the air in the example discussedabove-to 80 dry bulb and 30% relative humidity. In that case, the vaporpressure of water in the entering air would drop to 7.8 mm. Referringagain to Fig. 2, it will be seen that this corresponds to alithiumchloride solution concentration of about 37%. This means, that the spraysolution would change from a condition of 30% concentration to acondition of 37% concentration, corresponding to the above specifiedchange in the condition of the entering air. Such a change from 30% to37% concentration would take place, by a temporary evaporation of waterfrom the spray water to the circulating air, with a resultant increaseof the salt concentration in the spray unit, until the new condition hasbeen obtained. Conversely, should the relative humidity in the enteringair increase, then, there will take place a condensation from the airstream to reduce the concentration of the salts in the spray unit untilthe new equilibrium co-ndititon has been reached, and the unit thenbecomes stabilized at the new concentration. All the changesevaporationor condensation, as the case may beare automatic and require no controlof any kind.

During a change of conditions as described above, the unit affects therelative humidity in the space. It is, however, a situation which existsin a limited way and for a very short period, and is hardly of anyconsequence even if the unit be handling 100% of the circulated air.

Applicants have further discovered that the addition of lithium chlorideto the spray solution containing potassiurn permanganate alsosuccessfully accomplishes the second important object of this invention,namely, elimination of the use of a special dispenser to retard themixing into the main solution of the make-up potassium permanganate forreplenishing the consumed deodorant. Applicants have discovered thatpotassium permanganate in the form of crystals and sufiicient for ayears supply, can simply be placed in the retaining basket 16, which issub merged in the solution in the lower part of the compartment 11, andthat the lithium chloride in the solution acts to retard the solubilityof the potassium permanganate in the solution so as to maintain thecontent of the potassium permanganate in the solution within thedesirable concentration limit, even in the presence of an excess ofcrystals in the basket.

Without limiting themselves to any special theory, applicants believethat the action here is a complex function of solubility, dissociationconstants and water bound by Li Cl; primarily, it probably involves thetying up of water molecules by the lithium chloride molecules, the majorcomponent, thereby reducing the water available for dissolving the KMnOWhatever be the explanation, applicants have conclusively establishedthe reducing effect of lithium chloride solutions on the solubility ofKMnO in the following two ways:

l (a) By beaker tests. Excess potassium permanganate (more than 6% byweight) was added to three beakers, containing respectively (1)Distilled water; (2) 30% LiCl by weight in distilled Water, and (3) LiClby weight in distilled water at 80 F.

These were agitated at irregular intervals and held for periods varyingfrom hours to days to insure equilibrium between the crystals andsolute. KMnO concentration determinations were made by colormetricanalysis and also, by a wet chemical method involving ferrous ammoniumsulfate-ceric sulfate titration.

A number of these tests were made and representative results of the KMnOconcentration determinations were as follows:

Distilled H 0: 2 N or 6.3% by weight KMnO 30% LiCl: .125 N or 38% byweight KMnO, 40% LiCl: .09 N or 28% by weight KMnO,

The reduction of solubility of KMnO, by reason of the presence of thelithium chloride is quite evident.

(b) In a mobile washer used to prove the air sanitation eifectiveness ofapplicants system, there were added 300 grams of crystalline KMnO into awire mesh basket. The system contained 10 liters of liquid; hence, ifall the permanganate dissolved, the resultant uormality would be 1normal or 3% by weight of KMnO By chemical analysis, applicants havefound the operating normalities over a weeks time to range from .2 N-.18N or .62%.56% by weight of KMnO This system was run off and on for ayear under similar conditions with no evidence of overcharging with KMnOAn additional test was equally striking. When LiCl crystals were addedto a saturated (2 N or 6.2%) aqueous solution of KMnO the KMnO crystalsprecipitated, indicating the reduced solubility. When more water wasadded, this precipitate redissolved.

Practical experience with the type of deodorizing system underconsideration, i. e. one using a potassium permanganate solution, hasshown that in order to prevent corrosion and scaling, etc. of theequipment, the normality of the solution should not exceed .5. It isapparent from the data set out above, that the lithium chloride solutionwill maintain the normality at a value not in excess of .2, i. e. wellbelow this danger point.

From the foregoing, it will be seen that applicants have successfullyaccomplished the major objects of the present invention, namely (1)Inhibition of addition of moisture to the room air by the treatingsolution, and

(2) The necessity for using a special dispenser or other mechanicalcontrol device for limiting the dissolution of the deodorant chemical inthe treating solution, i. e. for controlling its concentration.

Applicants invention can be applied in a simple manner. It is merelynecessary to know the condition of the air to be treated, the dry bulbtemperature and relative humidity; the concentration of the lithiumchloride solution to be placed in the treating unit can then bedetermined in a simple manner by the use of the chart, as explainedabove.

By the use of a lithium chloride solution of a concentration as derivedfrom the chart, and carrying dissolved potassium permanganate, it ispossible to deodorizc air at room temperature without increasing therelative humidity in the room beyond the comfort zone. Also, there is nowaste of potassium permanganate as a result of excessive solutionthereof, and since the lithium chloride does not vaporize, it ispossible to operate the unit for long periods without adding eitherlithium chloride or potassium permanganate to the initial charge, andwith out any regeneration treatment. Further, since the treatingsolution has been adjusted to the proper concentration for thepredetermined design conditions of the system-air temperature andhumidity-the system will automatically stay in balance as far as thelithium chloride concentration is concerned.

While the operation of the present invention has been described withreference to the washer unit illustrated in Figure 1, it should beunderstood that the invention is not limited to the use of any specificsystem.

We claim:

In the process of deodorizing and sterilizing air circulated in occupiedenclosures by bringing the air in in- 10 timate contact with an aqueoussolution of potassium permanganate, the improvement of providing asubstantially long life for the permanganate solution which comprisesproviding a saturated permanganate solution having at least 6.2%permanganate by weight and having a normality of at least 2 N, andadding lithium chloride to the permanganate solution in an amounteffective to reduce the normality of the permanganate solution to belowabout 0.5 to thereby bring the concentration of the permanganatesolution to a strength less than saturation.

References Cited in the file of this patent UNITED STATES PATENTS552,142 Purves Dec. 31, 1895 1,971,777 Forrest Aug. 28, 1934 1,992,177Bichowsky Feb. 26, 1935 2,230,088 Podbielniak Jan. 28, 1941 2,683,074Kuehner July 6, 1954

